Aircraft control system



July 4, 1950 w. H. KLIEVER 25139493 AIRCRAFT CONTROL SYSTEMv Filed Sept. 17, 1945 rok/vf Y Patented July 4, 1950 UNITED STATES PATENT oFFicE I 2,513,493'7 i L AIRCRAFT coN'rRoL SYSTEM V Waldo H. Kliever, Minneapolis, Minn., -assignor Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., a corporation of Delaware This invention relates to the eld of aeronautical radio engineering and particularly to that phase of the art which concerns itself with instrument landing of air-craft. Various systems for insuring safe landing of craft at stations Where the Weather is overcast have been worked out but are found to have Various limitations and undesirable features, and it is .an object of this invention to provide a new and improved blind landing system obviating the difficulties of previous systems.

It is another object of this invention to provide a blind landing system in which the signal received in the craft is susceptible, without conf version, of operating a split phase alternating current motor.

It is another object of this inventionto provide a blind landing system in which a fixed transmitter. emits radiations having low frequency components in opposite phase relationships,.to gether with a further radiation establishing one of said low frequency components as a reference phase.

It is another object of this invention to provide. a blind landing system in which a receiver car.-l ried by the craft derives from a complex signal a pair of low frequency components, one of which. is established as a reference phase to which the l other is compared.

It is another object of this invention to provide a blind landing system in which a` transmitter emits radiations having low frequency components in different phase relations, together with a radiation establishing one of said low frequency components as a reference phase, while the receiver derives from the complex signal, made up of these various radiations a pair of low fre-- quency components one of which is established as a reference phase to which the other is compared. f

vide a blind landing system in Which three radiations are emitted at a common carrier frequency,

two of the radiations being modulated at a power frequency in opposite phase relation, while the It is a further object kof this invention to pro- ,l

vide a blind landing system in which a complex 11 Claims. (Cl. 343.-107) Wto derivea power frequency signal acting -a A further object of this invention is to pro-r'r signal is demodulated to derive a power frequency.

signal, which is in phase or out of phase with a reference phase, depending on the location of a less complex signal which is again demodulated the reference phase referred to above, the doubly f demodulated signal and the first mentioned signal operating the motory ofa rebalancinglindicator.

It is a further objectof this invention to prof vide a'blind landing system in which three radia.A i tions are emitted at a common carrier frequency, two of the radiations being modulated at a power frequency in- 4opposite phase relation while the `,third is doubly modulated to have a component of the power frequency and -in phase with the modulation of one of the singly modulated radiations, and in which a receiver tuned to the vcarrier frequency demodulates the complex signal` to zderive a power frequency signal, which is in I phase or 180? out of phase with a reference phase,v depending on the location ofthe receiver with. respectto the transmitter, and a less complex signal which is again demodulated to derive a power i frequency signal acting as the reference phase referred to above, the doubly demodulated signal andthe first mentioned signal operating the mo- 1 tor .of a rebalancingA indicator.

A still further object of our invention is a blind landing system in which a complex signal isv de-f modulatedto derive a power frequency signal,

which is in phase or 180 out of phase with a reff erence phase;4 depending on .the location of the from .the doubly demodulated signal.

A still further object of this invention is toprovide a blind landing system in which three radiations are emitted at a common carrier frequency, .tWo'of the radiations being modulated at E. a power `frequency in opposite phase relationship` fwhile the third is doubly modulated to have a component .of the'power frequency-and in phase with the modulation of one of the modulated radiations, together with a-receiver in which a complex signal demodulated to derive a power` frequencysignal, which is in phase or 180 out 1 of .phase with a reference phase, depending on `the locationof the receiverwith respect to the 'i transmitter, and a less complex signal which is` e again demodulated to derive a power frequency signal acting as the reference phase referred'tof" above, the doubly demodulated signal and the first-mentioned signal operating the motor of a I for: all radiation. A

pointed out with particularity inthe claims .an-`

nexed hereto and forming a part hereof. HOW- ever, for a better understanding of the invention, its advantages, and objects attained by its use, reference should be had to the subjoined drawing, which forms a further part hereofgand` to the accompanying descriptivey matter, .in which .I

have illustrated and describeda preferred em-v bodiment of my invention. f In the drawing, Figure 1 is a diagrammatic showing of a radio transmittersuitable for' use..

in my blind landing system;

Figure 2 is a similar showing of a receiver and indicator for use in my system, and

Eieure' is. a, diagram illustrative..ofthe.l phase.

distribution off; the-radiation sent. out. by my transmitter. Y l.

Referring Vfirst to Figure. 3,. IJ have.l shown. a radio.` transmitter Y locatedat. a point. O, with. re- Speet t0.. whichr three air-Craft are located at pointsPl., P2., and;P3-. From transmitterl O there, aresent out three radiations.,..by meansfwhich willjzpresently; begdescribed. The.:rst of these radiations. has a'directional. .pattern vfas; indicated atA, yand comprises alfty-megacycle carrier wave;mollulated;V at 400;vr cycles in afrst phase re.-

lationshin .A second. radiation Bisalso. emittedv by :transmitter Ov in a" space distribution similar. to, that of A, .but this radiation; while on acarrier frequency of. nityv megacycles,l modulated.. at..

400cycles in the. oppositefphase to. that modulating;A the:v radiation. A... third.noir-directional:-

radiation C" emitted-4 from: transmitter.. Q. com.-

prises a doubly modulated carrier. frequency of.; fifty. megacycles, the :first modulation being at.;l ten kilxocycles,y and y.the secondfmodulation beingA at 400 cycles in the; same. phat-seas.v radiation A;

The same' source. of carriernfrequencyfisz used .The craft :carries aradio .receiver tunedtothe carrier frequency ot .ifty..megacycles.,r andl includingfa; painof. demodulatorsthe. first ofi these demodulators-removinglthe carrier frequency so.. thatr its.- .outputjs as. composite cfa-10.0 vcy.cles...and modulated. tenkilocycles.. These 'two.ffrequencies..

are separated;v by.suitablef4 filters, and.` thel ten. kilocycle signalv is again demodulateda to..derivev 40`0L0y-olestherefrom. Since the '.llucyclelvoltage-carried as a; double.;mocl ulatiorr..orr thehcar.-

rier. frequency f is non-.directiona-lly radiatedg it..

will be receivedby thetransmitter, negardlessfof the positionofthecraft, anditherefore may be considered; aV standard z or reference phase.y

A .craft located; at. P2: receives appreciable A radiation.. from .both directional emitters; but 'duetogits position the .radiation receivedfromaemity terLfAexceeds thatreceived from emitter B; and` thecsingly. demodulateda, low. frequency is. therefore in -phase .With thev reference.

'lima craft locatedat point P3011- theslineO---Zr being available for comparison with the reference phase. If the transmitter isset up in such a fashion that the line Of-Z is along the desired .landing direction for aircraft, any craft following the zero signal line will be travelling in a proper azimuth for a correct landing at the station supervised by my invention. l

Ity will be appreciated, of course, thatA this invention relates only to the azimuth factor in blind landing systems, and that the glide factor may be, handled according to well known principles.

Referring now to Figure 1, it Will be seen that ina modulator l the output of a tenkilocycle oscillator Vll is modulated at 400 cycles from an oscillator l2. Inf a' second modulator I3 this modulated, voltage is `used to modulate the output of a fty megacycle oscillator I4, and the fdoublyY modulated voltage is amplified in am- On.- thelotherzhand, when the acraftis l,located atipoint;

theradiationsfrom emitters A and B are-equally received,. and. since theyfare opposite in-.phasev thyiucompletely cancel. out, .nofsignal therefore'.

plifler l5 and radiatedfrom a suitable nondirectional antenna L6.. At: thewsame` time,.in modulators H? and 2liv high frequency voltages. from the fifty megacycle. oscillator are; modulated.

with:400 cyclesfrom the-low frequency oscillatzn.` in 'opposite` phase relation, andV the. modulated. voltages are amplified in; amplifiers 2.4; 22;;- respectively.. A; pair of.l directional antennas. 23A.

and 2,4-, which-may. conveniently comprise. Yagi. arrays, are.- provided foruradiating the outputzof' amplifiers Z-l andi'2.-2.. radiation C in Figure 3, while radiationsA and B- inFigureBaretransmittedby antennas 2.4 and; 2.3, respectively. Oscillators,.. modulators,`

ampliiersrand directional .and non-directional..

antennas .are well Vknown tothoseiskilled in theart, and detailed construction of these-.familiar components of my invention is,-not,-herei included` The receiver shown inFigureZ of thedrawingcomprises a non-directional -antenna 25: energizing. a radio. frequencyfampliier andtuner. This unit istuned to ..f,ty megacycl'es, and itsloutput passesthrough.a-.demoduleator Z1: whose outputin v turn is amplified in an audio frequency amplifier.Z 30.'. The output of the audio amplier is fed.y to-a pairqoffl-lters 3l; and- 3'2, thelrst of which. passes alternating: current., of 4:00.. cycles. butpresents`l a high impedancetoalternating'currentfof lkil'oiy cycles, while lthe. secondllpresents al high-1 imped-#l ance to alternating voltage of tlllocyclesv but per'- mits 10 kil'ocyclezvoltage toipassfreelyi The cutputoflter32fis demoduiated-infa second demodula-tor 3'3fwhich may-also perform-an-amplifying function, and whose output energi-Zes-a phase-discriminator 3 4, a rebalancing arrangement 35; and

, one winding offa splitipliase motor` 36a l The-output oflter 3| alsofenergizesphase discriminator' 34 whose youtputlin turn;energizes-a:secondi windiing of motor 3.6.

' Demodulators, high and l'owfpassi-filters; amplifiers and tuners are individually well knownto those; skilled inthe art, and details of 'the structureof such units as are usedQin-myfinventionwill notnbegiven here. the salte ofi clarity,"however, it.' appears desirable tol-recite: in somedetail' the structure and relationship -of elements, 35i, and'36, and. this will nowfbeundertaken.

Motor 362-is off the-conventional 'splitbase. con-- struction. and comprises an armature 413'; carriedf* on a. shaft 4.15, and apair-of-eld`windings 42'fand .43, a.. condenserl 4'4f beingl connectedf in-parallel nected in series Lwith' winding` 43..

Antenna .I6 transmits thefk with winding. Wand a. condenserlllbeing con-- Thisseriescircuit is energizedifrom theoutput-ofdeinodulatcr 33,A which it willibeifrememberedis ccnstant'ih liphase. The-k capacitance of* condenser 45-`-is so# @hosen with respect'to the iriductance ofwinding 43' that the` circuit is :resonant at affrequency iif` 400 cycles: the current through: coil-43 is there-Y fore in phase with the voltage output of :demodulator 33. Similarly, the circuit includes winding 42 and condenser M is designed for resonance at 400 cycles. f

Rebalancing device The rebalancing device also comprisesa potential divider 54 havingaa resistance winding 55 and a contacting .slider 56.

transformer 50. 4I of motor 36, for actuation thereby, and mounted for unitary motion therewith is a pointer 51 moving Withrespect to a scale 60 to indicate the position of shaft; M

moment.

` Phase discriminator 34 is shown to comprise a pair of triodes 6I andY 62, whose cathodes areI joined to a common terminal 53 and whose grids are joined to a common terminal 64 and a transformer 65 having a'piimary winding 66 anda secondary 'winding 6l, center` tapped ati 10. Winding 42 of motor 361s energized from center tap 'l0 and terminal 63 through conductors?! and-12, respectively. Terminal 6 3 is connected with one output terminal of-lter 3| by conductor 13, and grid terminal 6! is energized from filter 3| and from potential divider 51% acting jointly, through a circuit which mayy be traced as follows; terminal- 64, conductor i4, slider, 56, winding 55, of potential divider-5,4, winding 5230i transformer 50, center .tapjtdand conductorl y'15.

The plates of triodes 6I and 5 2 arefenergized fromY the terminals of secondarywinding 61 of transformer 55. ,f ;v 2,

Operation The operation of the transmitter portion of my invention will be self-evident: 'from ther figure.

Oscillators Ii'and I2, modulator I0, oscillator I4," modulator I3, amplifierv I5, `andua'ntenna "|6"co .i operate to bring about radiationfpf a non'Y-dire'c4 tional, doubly modulated fiftyme'gacycl'ecarrier' signal. Oscillators l2 and Imodulator '20,'ampliiier4 22, 'and directional antenna 21%"cooperate toradiate a fty inegacycle ysignal modulated at 400 cycles in a'rst phase relationship and hav' ing a particular space distribution. oscillators I2 and I4, modulator il', amplier 2 l, and direc'- tional antenna 23 cooperate'y to radiate a fiftyVA megacycle carrier signal modulated at 400 cycles,`

in a phase 180 degrees spaced from that radiated by antenna 24, and in a space distribution which partially overlaps the radiation from antenna 24.'

Antennas 23 and' 2d are so placed as tobe less than one wave lengthofthe-'carrier frequency apart, and the antennas; are so arranged that the direction of` zero signal lies Aalong the direction'v in' which it is expected that the craft carrying the receiver will follow in landing.

The operation of my receiver is as follows, assuming that no other radiation on a fifty megacycle carrier is signicant at the instantaneous location ofthe receiving antenna. Antenna 25 receives the radiation from antennas I6, 24, and 23,', in relative intensities depending-upon the location of the receiving antenna with respectto the transmitting station.` This" cbmplex signal is 'Y amplified in unit 25', and demodulated in unit 21 to remove the carrier componenti?! rlffhe output of demodulator 21' therefore comprisesfa 'complex-1 audio frequency signalwhos :componentsin turn-f- 35, is shown to comprise a. transformer 50 having aprimary winding 5|l and. a secondary winding.52center. tapped asr at 53.l

Winding. 55 is connected across the terminals of secondary winding 52 of Slider 56 .is` mounted .on shaft,

at any givenk depend upon the location ofthe vcraftfwithv respect to the transmitting station. This complex. audio signal is amplied in unit 30 and transf mitted to filters 3| and 32.

The output from ampliner 30 comprises two` components, a simple 400 cycle component 'which` is of a rst phase or the opposite phase, depend ing upon the location of the receiving antenna with respect to the directional patternsent out. by radiations A and B, and a 10,000 cycle signal modulated at 400 cycles which is always in phase, with the 400 cycle signal derived from emitterA... Filter 32 is constructed to pass 10,000`cycle signals,` without substantial attenuation, and inpassing? the 10,000 cycle the 400 cycle modulation which is impressed upon it is also passed. The Aoutput. of filter 32, passes through demodulator 33 and the ten kilocycle component is removed from thef signal leaving only as400 cycle signal which is in phase with the signal transmitted fromvemitter A.

.The 400 cycle signal to which filter 32 presented,

a high impedance is transmitted throughiilt'erv 3| Without substantial attenuation, while filter 3| presents a very high impedance to a 10,000 yclej signal. It is thus apparent thatiilters, 3| arilltffv com-prise means for dividing the complex ,sigi'ialf derived from amplifier 30 into two portions fac-v cording to the frequencies of the portions, and' handling the` two portions separately inthe ensuing circuits. It Will also berealized that while the output of demodulator-33 is of a fixed phase,

the output of filter 3| reverses in phase asy'th'ea'irg craft passesfrom one side of yline 'O--Zftofthe' Other- ,The voltage across secondaryfwinding52 of transformer A5l), and therefore that across windtL -ing 55 of potential divider 54, has the frequency" and phase of the output of demodulatory 33; thatl is, it is in phase with radiation from emitter-"ALI When slider 56 is at the center of winding 55 no voltage derived from the secondary winding ap-f pears between the sliders of center tap 5?', and' conductors 'Mand15 simply comprise the con"-v ductive path'between lter 3| and the Igrids 'of` triodes 6I and 62. 'Howeven if sliderE-'is dis" placed' from the center of winding 55fin`,airs'td direction, va voltage is 'derived from the windingvl and impressed between conductors "Mand- 75 which `is of a rst phase relationship v'withrel-Q" spect to the voltage output of demodulator` 33',

while ifthe 'slider is displaced from the center of winding 55 in the opposite direction thefvolt-"I't age between conductors 'M .and "i5 is of theoppjoe site phase relation with respect to the output of demodulator I3. In either case, the'voltage derived from potential divider 54 is connected to add to the voltage derived from lter 3|, and 'y the sum of the voltages is impressed on the It will be realized' that if the two voltages are in phase, the'sum of grids of triodes 6| and 62.

the two voltages is greater than leither ltaken separately, and therefore the voltage derivedy from potential divider 54 augmente the signal' transmitted through the filter, while if the two position of slider 56 with respect to the center ol Winding 55.

Primary winding 66 of transformer 65 is ener-.f-i

, either triode.

plate of triodell'r will be. negativewhile tlriepiater.y

asians trlode El is positive and the plate of:triode-1lf In this/case, no current willilow .:to.- During' the next halfu cycle.l .theI

ist negative.

tion.' If 'the signal derived from filter-"il-v was-of' the opposite polarity,'so that the grids ofthe triodes' in turn were of opposite polarit-ieswith re-` spectto the plate voltages at the time just referred to', the'voltage'energizing Winding 42-Would be of the opposite phase relation, and the' motor would' operate vin ,the opposite direction;

For the case When the aircraft isrlocatedatv point 4PI with respect to the transmitter located atT (Ithe operation of the device isl asfollcws.

Substantially no energization from emitter; A is The output'from .filter received by the receiver; 3`I.is therefore out of phase with the `,output Yof the. demodulator. The grids of the triodes are'posi'- tivewhen plate 62 vis. positive. The motor is energized. tov run in` aforward direction. vShaftdll rotates. in a counterclockwise direction', so thatr indicator 'lfshows that the craft is tothe left'jof.;

the. proper course, and so that a feedback is.

derived from potentialv divider 541 Which Ais out `of phasewith the output .of demodulator 33. 1 Op;

eration of j motor dll continues .untill the feedback signalis equal in magnitude to the signals derived from Afilter 3l., at which point the signal voltage disappearsofrom the,.grid`s.of the triodes,anden# ergization ofwinding 42 is interrupted;` Motor 40 accordingly comes to a standstill.

When the craft. moves to position P2 with' re-yl spect. fto. transmitter. O, radiation. is. received'. from both emitters A andB, that. from transmitter A predominating. `In this. case,. the signal from filter 3l. phase Withtheoutput of democluev lator', the grids are positive when the. plate of' triode. 6l is positive, motor 40. runs i'nv a forwarddirection, shaft lll` movesl in .a counterclockwi'se direction, so that indicator .5l .indicates that the craft is tothe left ci thel desired course., andthe. feedback Voltage derived from. potential. din/iden 5L. -isout of. phase with-the-voltageoutput of .de-

modulator 33. Movement. .of motor llllcontinues., until .the signal on. the grids of. the anodes isi againreduced to zero, Whenv actuation .of the;4

motor is. interrupted.

It; observed from the structure .and operation of my'in-vent-ion recited abovaythatnthepower is required in.v the aircraft,4 nos. isi. vibrator orany converter means requiredtomake the signal derived; from the receiver useful operatethemotor. It:` will also. appreciated' tl-laty While4 xnyfzsystem` is adapted partieulariyy for' use in landing systems for aircraft, it isialsa useful whereser it' isudesiredto. provide reversiblaeactuation of:rv an :alternating current motor inzresponsei to reversible: signa1sintheform of 'radiationfrom,-A

aremote.transmitter; i

vliuinerous.obiieotsfandadvantages ot my inven= tion havebeen setzforth: inl the foregoing descrip tion, f togethery with.. details of the.V structurer and:

L function ofy thesinvention; andthe: novel thereof i are" pointed out` in the appended claims;v` The disclosure; however,y is illustrative only; andi I'imay make changessin detail, espcciallyin mat;

ter# of shape, size and arrangement of. panista 2Q; within the principle of the invention, to themlll@ extent indicated? bythe.v broad generalimeaning of thewterms-in which the: appended `claims are ex@ pressed. l f

Iclaim as..myinvention1: .Y

1.. InY apparatus ofl' the class described; in-i come bination: means emitting a plurality of correlate@- electroniagneticradiations, in theform ofimodurlated" high irequemiy.y waves of? a singlev carrier frequency, in a space distribution coordinated? With an-intell'genceto be'convey-edi; means yrel-f spcnsive tosai'dzel-ectromagnetic radiations; motorf meansfvaetuatedby sai'dresponsive means fnac-1 cordance v withl said l radiations; andindicating means-actuantedfoyA saidfmotor-means fory making-1 evident.: intelligence-derived leyl Said responsive' meansffrom; said"r radiations: said emitting-1meansf` comprising:` means non-directionaliy emitting/1a modulated electromagnetic radiation@ r ai. modulating component of fixed low frequency' and means directionall'y'femitting, simultaneously. with said.rstfnamedradiation, furtherrnodu- 4 latedelectrom'agnetic radiations having modulat-V componentsofsaidlow frequency, one of'said a. iii-st of. said pluralityv of radiations andlthere' sultantof the modulating. components.` of,others signalV received. in. the craft is. ofsuch a naturethat in itself it comprises a satisfactorymedi-um..

for; .energizing motor 3.6. No special source.; .of

componentsbeing in phase andthe other being. v

180. outA of. phasewithsaidcomponent oi'said." Yfirstenamedradiatoni.

2; m apparatus @finie class described; in com! bnation means` emitting .,aplurality. of. correlated] electromagnetic radiations..in` the` form of modui. latedhigh frequencywaves ofja single carrier .fre-.-

, with said radiations and' indicating means' actu.-

atedhy saidr motor .means for making evident. in#V telligence -deriwedihy said responsive means said radiations z. saidresponsive means. comprising.` meansr energizing .said4 motor in. accordance witll theYrelati-on beimszeena modulating, componentoff.

of said plurality otradiaticns.v

3.'. Innapparatus of theclass described, in com- ,binationc a transmitterl comprising means noni'rnaazxaiY radiation.; andA a receiverl comprisinrem versible motor means Idesigned for= energization with alternating voltage of said fixed frequency, indicatcrfvm'eans actuated by said motor, and motor control means responsive to said electromagnetic radiations for causing energiz-ation. of saidmotor in accordance with the relation between said first-named component and the resultant of said two second-named components.

. 4. In a device of the class described, in combination: a first source of alternating voltage of a power frequency; asecond source of alternating voltage of an audio frequency; a third source of alternating voltage of a radio frequency; first means modulating vsaid radio frequency voltage by said power frequencyvoltage to provide va first modulated voltage; second means modulating said radio frequency voltage'by said power frequency voltage to provide a second modulated voltage, said power frequency voltages said first and second modulating means being 180 out of phase; means modulating said audio frequency voltage by said power frequency voltage to'provide a third modulated voltage; means modulating said radio frequency voltage by said third modulated voltage to provide a doubly inodul'ated voltage, and means electromagnetically radiating said i"1rst.and second modulated voltages and said doubly modulated voltage in selected iield intensity patterns.

.5.11m a device of the class described, in combination: a first source of alternating voltage of a power frequency; a second source of alternating voltage of an audio frequency; a third source of alternating voltage of a radio frequency; iirst means modulating said radio frequency voltage by said power frequency voltage to provide a first modulated voltage; second means modulating said radio frequency voltage by said power frequency voltage to provide a second modulated voltage, said power frequency voltages in said first and second modulating means being 180 out of phase; means modulating said audio frequency voltage by said power frequency voltage to provide a third modulated voltage; means modulating said radio frequency voltage by said third modulatedl voltage to provide a doubly modulated voltage; means electromagnetically radiating said doubly modulated Voltage non-directionally; and means electromagnetically radiating said first and second modulated voltages individually in selected overlapping directional patterns.

6. In apparatus of the class described, in combination: means directionally emitting a first electromagnetic radiation having a modulation of a selected frequency and phase; means directionally emitting a second electromagnetic radiation having a modulation of said frequency and of the opposite phase, the field strength pattern of said `first and second radiations partially overlapping; and means nondirectionally emit ting a third electromagnetic radiation having a modulation component of the frequency and phase of the modulation of said first radiation, so that the eld strength patternA of said third radiation overlaps the patterns of said first and second radiations.

7. Means for responding to a signal voltage having a low frequency component of variable amplitude and reversible phase and a modulated high frequency component of fixed phase and amplitude, the modulation being of said low frequency and of xed phase, comprising, incombination: means deriving said signal voltage; means separating said low frequency component from said high frequency lcomporlent'to pren/'ideA low frequencyimotor; almotor;controlidevicehave powerf circuit; meansisenergizing said powerA ciriv cuit in accordance:witlizsaidzcomparison voltage;

means energzingssaid input circuit in accordance` with said `variablevoltag'e andi'w'ith alva'riable portion of -said' comparison voltage; means e`n. ergizing said `motor I in' 'accordance only with the output 'from saidl `devicel and `with said comparison voltage ;y 1 means: varying the magnitudef and reversing the?. phase of said variable portion by operation' of said motor; 1 and means rfpositioned bysaidmotorm ser.,

i 8. Meansi forrespondingr to a''signal'fvoltag'e: having a low frequency;componenti"ofwvariable amplitude and l'reversible phase'iand'. awmodulated high frequency component of. fixed phase: andv amplitude; they modulation being; of saidl low? frequency and .ofxed phase, comprising, ...in combination: meansderiving said 'signal voltage; means separating saidy low frequency `component from! said `'high frequency Vcomponent -to, provide a'wvariable low frequency voltage;A means-der modulating *said hig-lff:l frequency component-.to provide a comparison flow. frequency voltagef a low frequencyf-motori a''motor controlfedevice: having an input circuit, an output circuit, and a power circuit; means energizing said power circuit in accordance with said comparison voltage; a voltage divider adjusted by said motor; means energizing said voltage divider in accordance with said comparison voltage; means energizing said input circuit in accordance with said variable voltageand with the output of said voltage divider; means energizing said motor in accordance with the output ofsaid divider and with said comparison voltage; and means positioned by said motor.

9. Means for responding to a signal voltage having a low frequencyucomponent of variable amplitude and reversible phase and a modulated high frequency component of fixed phase and amplitude, the modulation being of said low frequency and of fixed phase, comprising, in combination: means deriving said signal voltage; means separating said low frequency component from said high frequency component to provide a variable low frequency voltage; means demcdulating said high frequency component to provide a comparison low frequency voltage; a low frequency motor; a` motor control device having an input circuit, an output circuit, and a power circuit; means energizing said power circuit in accordance with said comparison voltage; means energizing said input circuit in accordance with said variable voltage and with a variable portion of said comparison voltage; means energizing said -motor in accordance only with the output from said device and with said comparison voltage; means varying the magnitude and reversing the `phase of said variable portionby operation of said motor; and an indicator actuated by said motor.

10. Means for responding to a signalvvoltage having a low frequency component of variable amplitude and reversible phase and a modulated high frequency component of fixed phase and amplitude, the modulation being of said low frequency and of xed phase, comprising, in combination: means deriving said signal voltage; means separating said low frequency component 11' Y ttbm-said .highreguency nennipunent'to provide: a.r

intimacy-vonage; marinsy Vdez'rxmzlubiting-.saidrhigh frefmefncy cumpcmenttopmirde' ar comparison rlowirequencyfwoltage; :la low tire-l quartier;y .meter having' `ar-pxr 'ofw-indingsiinf space wwaturezeiphasediscminaztur haungean inmit circuit, ran mxtput circuit and 'powerfcinenergizing power 'fcircuit in itceordance with *said cxnnpxtrlisorrrV voltage; means enzxgizing said input in `accordance with amil variable voltage and,-wrtl'iu'aA variable portion ecom'parison voltage ,'means'energizing'one winding of' 'sadvmotor in .accordance-,with :the outputafmm said zdiseriminatm'; "means energizing theeother winingeu: said motor in'accordance wtnfmdzcomparism'vo1tage-;;,means tirar-ying .the

' magnitude and reversing the phase 'ebend-vari tbleportionffby aperationof said motor; and meins positionedzzbyisaid'motor.

"511.311 V:covmbinatinm;: means directionallymdiatingf'electmmagneticfaignalsin overlapping patterns; having 1.a rectilinrzeare1-.ruimtental V line, said signahhavinga commonfearrier'fxtequency and a; cammen ,modizl'atmrifrequencm the `xrxciciuletons' beingv uffnppositeifphase; means norr-'direetiorially.V

limiting a doubly modnkated 4'e1'ec'trfrmagnetic l 'signal =ieoxnpifrsii'igfthe jtsame :carrier :frequency modulated at# an :intennedi'ate frequency whichil :mudisited yat.` 'saidveomrmorr modulation frequency'in'phasewith themodulation-iof one f 24u-reges 5, lated signal.

12 of said.4 direetonally radiated signals;.\andx'e1v ing: responsive tothe-relativsms'rip 'of the sum of-said directenally radiated signals Vt0 the lowest frequency component .vof :said doubly mo'hx-l WALDO REFERENCES CITED "The fol-lowing references Vaire of record 1n the l0 'le-of this patent:

UNITED 'STATES PATENTS Number Name Date 17,961,206 Diamond June 5, 1934 15 1,985;0&6 Marrson -Decv. 18, 1934 v*2,144,293 Shankiin fJazn. 17,1939 `2,165,304 f Runze ;Ju}y `11,1939 '2,183,725v @Seeley ,13e :.19f,V 1939 i2,236;374. vvMarrison Mar. 25,1941 20 -2,256,482 Isbister Sept; 23, 1941 2,25;487 Moseley Sept.'23, V1941- y2,288,815y Luck July' 7, v 1942 251145093 Landon Mar.1-6,.1943. '2,433,195 Bond Dee. 123, 1947 25 438,288 .Jaeobson;et.a1.. 23,1948 .2,1440j'155 "OBren May 4,1948

l yF05REIGN PATENTS Number Country .Date 0 547,183 .GreatBrtain Aug. 17,-A 1942 vGreat yBritain Aug. `22, 194D 

